staging: panel: Fix single-open policy race condition

Fix the implementation of a single-open policy for both
devices (lcd and keypad) by using atomic_t instead of plain ints.

Signed-off-by: Mariusz Gorski <marius.gorski@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/panel/panel.c b/drivers/staging/panel/panel.c
index 98556ce8af6afe8c85a7fc22d996cb2a0c6a0b09..d30ccb594785755ba96eae4c0b59a6b59bbe32ae 100644 (file)
--- a/drivers/staging/panel/panel.c
+++ b/drivers/staging/panel/panel.c
@@ -404,8 +404,11 @@ static unsigned char lcd_bits[LCD_PORTS][LCD_BITS][BIT_STATES];
 #endif /* DEFAULT_PROFILE == 0 */
 
 /* global variables */
-static int keypad_open_cnt;    /* #times opened */
-static int lcd_open_cnt;       /* #times opened */
+
+/* Device single-open policy control */
+static atomic_t lcd_available = ATOMIC_INIT(1);
+static atomic_t keypad_available = ATOMIC_INIT(1);
+
 static struct pardevice *pprt;
 
 static int lcd_initialized;
@@ -1347,7 +1350,7 @@ static ssize_t lcd_write(struct file *file,
 
 static int lcd_open(struct inode *inode, struct file *file)
 {
-       if (lcd_open_cnt)
+       if (!atomic_dec_and_test(&lcd_available))
                return -EBUSY;  /* open only once at a time */
 
        if (file->f_mode & FMODE_READ)  /* device is write-only */
@@ -1357,13 +1360,12 @@ static int lcd_open(struct inode *inode, struct file *file)
                lcd_clear_display();
                lcd_must_clear = 0;
        }
-       lcd_open_cnt++;
        return nonseekable_open(inode, file);
 }
 
 static int lcd_release(struct inode *inode, struct file *file)
 {
-       lcd_open_cnt--;
+       atomic_inc(&lcd_available);
        return 0;
 }
 
@@ -1627,20 +1629,19 @@ static ssize_t keypad_read(struct file *file,
 
 static int keypad_open(struct inode *inode, struct file *file)
 {
-       if (keypad_open_cnt)
+       if (!atomic_dec_and_test(&keypad_available))
                return -EBUSY;  /* open only once at a time */
 
        if (file->f_mode & FMODE_WRITE) /* device is read-only */
                return -EPERM;
 
        keypad_buflen = 0;      /* flush the buffer on opening */
-       keypad_open_cnt++;
        return 0;
 }
 
 static int keypad_release(struct inode *inode, struct file *file)
 {
-       keypad_open_cnt--;
+       atomic_inc(&keypad_available);
        return 0;
 }
 
@@ -1663,7 +1664,7 @@ static void keypad_send_key(const char *string, int max_len)
                return;
 
        /* send the key to the device only if a process is attached to it. */
-       if (keypad_open_cnt > 0) {
+       if (!atomic_read(&keypad_available)) {
                while (max_len-- && keypad_buflen < KEYPAD_BUFFER && *string) {
                        keypad_buffer[(keypad_start + keypad_buflen++) %
                                      KEYPAD_BUFFER] = *string++;